This image shows a large bile duct (BD) and one of its tributaries (Br D). A large artery (Art) is present for comparison. The smaller duct is lined with simple cuboidal to columnar
epithelium; the larger duct is big enough that the epithelium is
beginning to stratify, and a stratified columnar epithelium can
frequently be seen in ducts that size and larger. There's an extensive
supporting investment of CT around both of the ducts.
The duct system in the liver is set up pretty much like any other exocrine gland's would be, and if you wanted to classify it structurally, it would be a compound form. Most species have two main ducts that carry the bile produced out of the substance of the liver, and convey it to the intestine (or possibly the gall bladder, in those animals that have one). These two ducts are joined together at some point out of the plane of this section, and the smaller one is a tributary of the larger.
Monkey liver; H&E stain, 1.5 µm plastic section, 200x